The present invention relates to flow control devices employed for regulating the volumetric flow of fluid in a conduit over a range of variable supply line pressures. The present invention relates in particular to devices for controlling the flow of fluid supplied to appliances such as household washing machines and dishwashers. Household appliances of this type commonly employ an electrically actuated water inlet valve for controlling the amount of fluid admitted to the appliance during the operating cycle when the appliance is connected to the household water supply line. Typically, the amount of fluid admitted to the appliance is determined by opening the inlet valve for a timed interval. If the flow rate is known and is substantially constant, the amount of fluid admitted or water fill is determined by permitting the known flow rate for predetermined interval.
Thus, it is important when the aforementioned technique is employed for controlling water fill in household appliances, to maintain a known or constant rate of inlet flow over the interval of time during which the electrically controlled inlet valve is maintained in the open position. Since the supply line pressure to a household may vary over a broad range of pressures determined by the particular water supply system available at the location of the household, the inlet valve must, of necessity, have some means of maintaining the flow rate at a nearly constant value over the range of supply line pressure encountered in actual service conditions. It has thus been the practice of manufacturers of household washing appliances to include a flow control device at the appliance water inlet. In particular, it is known to provide a resilient, deformable flow control washer at the inlet of the electrically actuated fill valve.
The resilient flow control washer is typically received in a cavity conformed to closely fit the flow washer. Upon experiencing increased line pressures at its upstream face, the flow washer is deformed elastically by the action of the pressure against flow washer and the reaction of the cavity wall. The elastic deformation of the flow washer upon experiencing increased pressure characteristically reduces the size of the flow orifice through the washer, and thereby maintains the flow rate constant through a reduced size flow orifice.
Where resilient flow control washers are employed having a single central flow orifice or a plurality of circumferentially spaced flow orifices, it has been found that at higher inlet pressures, and consequently greatly reduced size orifices, cavitation and noise are encountered as the higher velocity flow passes through the orifice. Thus, it has long been desired to provide a resilient elastically deformable flow control washer which provides the desired flow control over a broad range of inlet pressures and yet does not experience cavitation or noise at higher pressures.